Fiberglass comes in many shapes and sizes and can be used for a variety of applications. A general discussion of fiberglass manufacturing and technology is contained in Fiberglass by J. Gilbert Mohr and William P. Rowe, Van Nostrand Reinhold Company, New York 1978, which is herein incorporated by reference. During the preparation of fiberglass, whether by a blown fiber or continuous filament manufacturing process, the resulting glass fibers may easily be degraded in their strength characteristics by the self-abrasive motion of one fiber passing over or interacting with another. As a result of this self-abrasion, surface, defects are caused in the fiberglass filaments resulting in reductions in overall mechanical strength. Furthermore, fiberglass which is destined for use as building insulation and sound attenuation is often shipped in a compressed form to lower shipping costs. When the compressed bundles of fiberglass are utilized at the job site, it is imperative that the fiberglass product recover a substantial amount of its precompressed thickness. Otherwise, loss of insulation and sound attenuation properties may result.
Traditionally, fiberglass has been treated with phenol/formaldehyde resole binders to alleviate the previously-mentioned defects. The phenol/formaldehyde binders utilized in the past have been the highly alkaline resole type which have the combined advantages of inexpensive manufacture and water solubility. Typically, the binders are applied to the fiberglass from aqueous solution shortly after the fibers have been produced, and cured at elevated temperature in a curing oven. Under the curing conditions, the aqueous solvent is evaporated, and the phenol/formaldehyde resole cures to a thermoset state. The fibers in the resulting fiberglass product are thus partially coated with a thin layer of thermoset resin, which tends to accumulate at the junctions where fibers cross each other. The resulting product therefore not only suffers from less self-abrasion, but also exhibits higher recovery than a fiberglass product not incorporating a binder.
The alkaline phenol/formaldehyde resoles contain a fairly large excess of formaldehyde from the manufacturing process. This excess of formaldehyde has been taken advantage of by adding urea to the phenol/formaldehyde resole, resulting in a urea-extended resole. Urea-extended phenol/formaldehyde binders are more cost-effective than the straight phenol/formaldehyde resins, but exhibit some loss in properties as the urea content increases.
The urea added in urea-extended phenol/formaldehyde binders serves the dual purpose of increasing useable solids content at minimal cost as well as lowering formaldehyde emissions during application of aqueous solutions to fiberglass from the spinning process as well as during elevated cure to the thermoset state. The amount of urea which can be added to the phenol/formaldehyde resin is limited, however.
If the amount of urea added is too high, the performance of the product, particularly with respect to recovery from compression and rigidity, and especially after storage under humid conditions, will be decreased. The amount of urea-extension possible is generally limited to a maximum of approximately 70:30 phenol/formaldehyde solids to urea for this reason. It would be desirable to be able to increase the amount of urea without sacrificing physical properties of the fiberglass product, as urea is considerably less expensive than the phenol/formaldehyde resin itself.
Traditional alkaline phenol/formaldehyde resole resins are manufactured with a large excess of formaldehyde to lower residual phenol to low levels and to insure complete water solubility of the product. Addition of urea to such a product causes a complex reaction in which many polymeric species are produced, both through reaction of urea with methylolated phenols, formation of methylolated ureas followed by reaction with the phenol/formaldehyde resin, and formation of urea/formaldehyde polymeric species. As the amount of added urea approaches the amount of excess formaldehyde on a stoichiometric basis, formaldehyde emission levels drop appreciably. However, formaldehyde is still emitted, even at 1:1 stoichiometry. Moreover, as formaldehyde levels decrease, ammonia emissions increase. Adding urea above that required on the basis of stoichiometry lowers formaldehyde emissions even more, but increases ammonia emissions and moreover, causes an intense amount of "blue smoke" which makes this larger amount of urea unusable, even where increased ammonia emissions can be tolerated. It would be desirable to increase the amount of urea which can be utilized to extend alkaline phenol/formaldehyde resole resins without increasing ammonia emissions and without increasing "blue smoke."
Phenol/formaldehyde resole resins are generally alkaline. Acid catalyzed novolac resins have been used to prepare binder compositions, but their use is problematic, as the novolac resins are not sufficiently water soluble and must be used as dispersions. For example, U.S. Pat. No. 3,956,204 discloses anti-punking resins prepared from phenol and less than equimolar formaldehyde under acidic conditions, where large quantities of 2,2'- and 2,4'-dihydroxydiphenylmethanes are produced. Following resin preparation, a nitrogenous substance is reacted in and the composition is optionally extended with urea following which the pH is adjusted to between 7 and 8 prior to application to the fiberglass and subsequent cure.
U.S. patent application Ser. No. 07/574,014, a copy of which is available from NTIS, discloses the preparation of phenol/formaldehyde resins employing low levels of excess formaldehyde and an amino-functional co-reactant which may be urea or a substituted urea, under acidic conditions employing aluminum sulfate or mineral acid as a catalyst in resin preparation. However, although the resin synthesis takes place under acidic conditions, the resin is neutralized prior to cure. The resin is stated to be useful for preparing particle board and other wood products. However, the products do not appear suitable for application to fiberglass as a binder.
U.S. Pat. No. 3,701,743 discloses a modified urea/formaldehyde resin as a plywood adhesive, prepared by blending together a urea/formaldehyde resin and a minor amount of a phenol/formaldehyde resin, together with an amylaceous extender, and curing in the pH range of 5-7. Aluminum sulfate in an amount of approximately 1% based on total solids is the preferred curing agent, and is said to eliminate bleed-through of the resin through the surface veneer. The use of an amylaceous extender raises the potential for microorganism growth, and the high proportion of urea/formaldehyde resin renders the composition unsuitable for application to fiberglass.
In U.S. Pat. No. 3,039,981 is disclosed a metallized phenol/formaldehyde resin prepared by combining a phenolic resin with aluminum sulfate or other ionic metal compound at elevated pH, following which the insoluble resin is emulsified with mineral oil and applied to fiberglass.
Great Britain Patent No. GB 2245578 discloses the co-use of ammonium sulfate and aluminum sulfate in the cure of phenol/formaldehyde resins and other formaldehyde resins. No urea-extended resins are disclosed. The reference indicates that aluminum sulfate alone is unsatisfactory. A separate curing solution containing ammonium sulfate, aluminum sulfate, and a sufficient minor amount of urea to prevent precipitation of the less soluble ammonium aluminum sulfate inner salt is suggested. The amount of catalyst solution ranges from 5% to 10%, which correlates to an aluminum sulfate content in the uncured resin of about 0.7% to 1.3% by weight.
Ammonium sulfate has been used as a latent catalyst in the cure of phenol/formaldehyde binders. Ammonium sulfate is the salt of a strong acid and weak base and therefore hydrolyses in aqueous solutions to produce an acidic solution. However, when added to an alkaline phenol/formaldehyde resole, the solution remains basic due to the initial alkalinity. The ammonium ion can react with excess formaldehyde to form hexamethylene tetramine and sulfuric acid, thus further lowering the pH. However the pH drops only to about 6.5 during this process, and importantly is both time and free formaldehyde dependent. Thus, addition of ammonium sulfate to alkaline resoles for use as a catalyst may produce varied results depending upon both the initial free formaldehyde content of the resin as well as the time the catalyzed resin is allowed to stand prior to use.
It is an object of the subject invention to reduce formaldehyde and ammonia emission levels in a process for coating fiberglass with a urea-extended phenol/formaldehyde binder solution.
It is a further object of the invention to enable the use of higher levels of urea in urea-extended phenol/formaldehyde fiberglass binder solutions without experiencing a loss in physical properties of the fiberglass product.